There is provided a mobile telephony device, comprising a mobile station that can be connected to a mobile telephony network by using a SIM card. A multiplexer can be connected to the mobile station, the multiplexer holding several SIM cards. An exemplary multiplexer may comprise a first switching component that is configured such that each one of the SIM cards can be connected to the mobile station. The exemplary multiplexer may comprise a second switching component that is configured to switch off the mobile station while one SIM card is being disconnected from the mobile station and another SIM card is being connected to the mobile station.